Liquid crystal display apparatus is a passive light-emitting device, which does not emit light itself and requires a backlight module to provide its liquid crystal panel with a light source such that it displays images. Since the backlight module used in the liquid crystal panel has the characteristics of being light and thin and saving power, it is widely applied in display apparatuses.
At present, backlight module techniques mainly used by the liquid crystal display apparatus are Cold Cathode Fluorescent Lamp (CCFL) and Light Emitting Diodes (LED).
Since LED backlight module has many advantages such as high luminance, high color purity, long life, good reliability, being free of mercury pollution, and so on, there is a gradual increase in the proportion thereof in backlight modules.
LED backlight modules can be classified into direct-type and side-light type in the light of optical structure. Light sources are placed at side faces of the panel of the side-light type LED backlight module, whereas for the direct-type, light sources are placed below the panel. As shown in FIGS. 1 and 2, FIG. 1 is a schematic diagram of a direct-type backlight structure in the prior art; FIG. 2 is a manner of arrangement of LED lamps in the direct-type backlight in the prior art. The direct-type LED backlight module mainly comprises: backplane 01, circuit board 02 within the backplane 01, LED lamps 03 distributed at intervals, bottom reflection sheet 04, diffusion plate 05, optical diaphragm 06, side reflection sheet 07, prism sheet 08, and the like.
The light emitted from the LED lamps is a point light source. Due to light-emitting angles of the light, it may easily occur that the light intensity of the backlight module in a certain angle direction is relatively strong, while the light intensity thereof in another angle direction is relatively weak.
In the prior art, uniform illumination is usually achieved by increasing the number of LED lamps or increasing the light mixing distance (which usually refers to the distance H from the top of the bottom reflection sheet 04 to the bottom of the diffusion plate 05) of the backlight module. This leads to an increase in the cost or thickness of the backlight module. Furthermore, when there are a fixed number of LED lamps in the backlight system, if the thickness of the backlight module is reduced, non-uniformity of the light incident on the display panel would be caused such that obvious light spots will appear on the display apparatus.